Patchwork [2/2] ARM: tegra: Use DT /cpu node to detect number of CPU core

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Submitter Hiroshi Doyu
Date Jan. 14, 2013, 7:52 a.m.
Message ID <>
Download mbox | patch
Permalink /patch/211721/
State Changes Requested, archived
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Hiroshi Doyu - Jan. 14, 2013, 7:52 a.m.
SCU based detection only works with Cortex-A9 MP and it doesn't
support ones with multiple clusters. The only way to detect number of
CPU core correctly is with DT /cpu node. If DT /cpu node based
detection fails, we just simply fall back a single core in Tegra SoCs.

Signed-off-by: Hiroshi Doyu <>
Based on the discussion:
 arch/arm/mach-tegra/platsmp.c |   17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)
Russell King - ARM Linux - Jan. 14, 2013, 9:27 a.m.
On Mon, Jan 14, 2013 at 09:52:50AM +0200, Hiroshi Doyu wrote:
> +	if (!arm_dt_cpu_map_valid())
> +		set_cpu_possible(0, true);

You don't need to do any of this (and, therefore, I don't think you even
need the first patch.)

The generic boot code will set CPU0 as possible, present and online.  Think
about it: you're booting on that very CPU so it better be possible, present
and online.  If it isn't, what CPU is executing your code?

arm_dt_init_cpu_maps() will only ever set _additional_ CPUs in the possible

Ergo, by the time the above code is run, CPU0 will already be marked as
possible.  Therefore, the above code and arm_dt_cpu_map_valid() is not
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diff --git a/arch/arm/mach-tegra/platsmp.c b/arch/arm/mach-tegra/platsmp.c
index 6867030..456e7cc 100644
--- a/arch/arm/mach-tegra/platsmp.c
+++ b/arch/arm/mach-tegra/platsmp.c
@@ -24,6 +24,7 @@ 
 #include <asm/mach-types.h>
 #include <asm/smp_scu.h>
 #include <asm/smp_plat.h>
+#include <asm/prom.h>
 #include <mach/powergate.h>
@@ -177,22 +178,10 @@  done:
 	return status;
- * Initialise the CPU possible map early - this describes the CPUs
- * which may be present or become present in the system.
- */
 static void __init tegra_smp_init_cpus(void)
-	unsigned int i, ncores = scu_get_core_count(scu_base);
-	if (ncores > nr_cpu_ids) {
-		pr_warn("SMP: %u cores greater than maximum (%u), clipping\n",
-			ncores, nr_cpu_ids);
-		ncores = nr_cpu_ids;
-	}
-	for (i = 0; i < ncores; i++)
-		set_cpu_possible(i, true);
+	if (!arm_dt_cpu_map_valid())
+		set_cpu_possible(0, true);